The present invention is directed to a safety device which is designed for controlling or limiting within a machine the axial operating load exerted on a drive worm, wherein the drive worm is mounted on a rotary main shaft having one end which is provided with a connecting means for connecting the shaft to a drive shaft, said main shafting having a second end being coupled to the safety device by a non-rotatable auxiiiary shaft wherein the safety device allows an axial shifting of the drive worm to cause an uncoupling of the first end from the drive shaft in response to an excess torque being applied to the worm.
Cutting presses, such as illustrated in FIG. 1, are known to be provided with safety devices. The press in FIG. 1 includes a frame Ba that consists of lateral stays or frame members H, an upper crossbar of frame member Ts and a lower crossbar or frame member Ti. An upper fixed beam or platen Ss is mounted on the upper crossbar Ts and a lower movable beam or platen Si is provided within the frame. A sheet F of material, such as pasteboard or cardboard, which is to be cut by cutting rules Fi of a tool O fitted on the upper beam or platen Ss is to be carried between the two platens Si and Ss by a gripper bar Bp, which is carried by a pair of chains (not illustrated). In the course of the cutting process, the lower beam Si is moved by an assembly consisting of a drive worm 1, a gear R engaging the worm 1, a crankshaft Vi and toggle levers G. With rotation, the crankshaft Vi moves from a lower dead center position, as illustrated, to an upper dead center position and back. The drive worm 1 is driven by a motor M. The connection between the motor M and the drive worm 1 is achieved by means of a drive belt C, a brake and clutch assembly E, a flywheel Vo and a safety clutch or connecting means consisting of a toothed rim 30 mounted in a toothed socket of a shaft 5 of a flywheel Vo and a toothed part 10 which is arranged on a first end 12' of a main shaft 12 of the drive worm 1. The shaft 12 is fitted so as to be rotated freely and shifted lengthwise in the frame Ba of the machine. At the second end 12", the shaft 12 has a safety device S', which acts to limit the axial load on the shaft 12 and consists of a non-rotary shaft end 4 connected by a clutch support 11 to the shaft 12 of the drive worm 1. This end of the shaft 4 is held in place by a tapering lock S1 engaged with a corresponding groove S3, which are located on the same end of the shaft 4. The locks S1 are pushed toward the groove S3 by springs S2. As soon as the torque exerted on the drive worm 1 becomes too strong under the effect of an axial pushing force resulting therefrom, the drive worm 1 will undergo a shift and, thereby, push the ends of the shaft 4 toward the lock S1, which then move apart by compressing the springs S2. With a certain amplitude of the axial force exerted, the locks will now cease to be engaged with the end of the shaft 4 so that the toothed part 10 on the first end 12' of the shaft 12, will slip out of the toothed rim 30 of the shaft 5 to disconnect the shaft 5 from the shaft 12.
The safety device mentioned above is necessary in a sheet processing press to compensate for problems caused by the following:
a jam-up, which might happen somewhere within the press and cause a displacement of the chain pair carrying the gripper bars Bp through the press. This will involve the risk that the bar Bp will become caught between the two platens Si and Ss when the toggle lever G and the crankshaft Vi reach the upper dead center position; PA1 some matter or tool might have been left between the two beams of platens Si and Ss after mounting the tool O or its counterpart (not represented); PA1 two sheets F might be simultaneously carried into the machine by accident; and PA1 for an unknown reason, an excessive force might build up and exert a high torque on the drive worm 1. Such an occurrence is possible with a high number of blanks to be cut simultaneously involving too high a processing force.
U.S. Pat. Nos. 902,527 and 2,467,426, along with French Patent 1 337 828 all disclose other examples of known safety devices which allow for controlling the axial loading on a drive worm.
The devices known up to now for controlling the axial load exerted on a drive worm do meet the required safety conditions properly speaking, for instance, in the case of cutting presses, the safety device S' allows a sufficiently safe and quick disengagement of the drive worm 1 from the drive system of the flywheel Vo and the motor M when an axial overload occurs. However, these devices have a drawback in the event that they will have to be put back into operating position or reset after the axial overload has been removed. This resetting results in a long machine down-time, which may last for one or two hours. Since it is desired to increase the production speed of a machine to its maximum, an interruption of this duration is no longer permissible or desirable.